Chillida's graphic work, like his sculpture, shows a preoccupation with form, space and framing. Martin van der Koelen has described Chillida’s main concern as “the concept of space and its determinedness by formed matter, the relation between emptiness, volume and their mutual limits”. Absence is therefore as important as presence. The balance of dualities in his work such as black-white, heaviness-lightness and emptiness-fullness give Chillida’s work a universal importance.